Solar water heating system

ABSTRACT

The present invention relates to a solar water heating system including: a solar collector to which solar heat is collected; a solar collector circulation pipe adapted to circulate an operating medium on which the solar heat collected by the solar collector is accumulated therealong; a thermal storage tank in which the operating medium and the water used for living are heat-exchanged; a hot water circulation pipe communicating with the thermal storage tank; a freezing prevention valve located on one side of the hot water circulation pipe and adapted to be open and closed to allow the water in the thermal storage tank to selectively flow along the hot water circulation pipe; and a controller adapted to control the operation of the freezing prevention valve, thereby preventing the hot water circulation pipe from being frozen and destructed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of International Application No. PCT/KR2011/001507 filed on Mar. 4, 2011, which claims the priority to Korean Application No. 10-2010-0020141 filed on Mar. 5, 2010, Korean Application No. 20-2010-0004101 filed on Apr. 20, 2010, and Korean Application No. 10-2010-0063074 filed on Jun. 30, 2010, which applications are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a solar water heating system, and more particularly, to a solar water heating system that can produce hot water through the heat collected from solar energy, while being simple in configuration, substantially high in heat efficiency, and further providing all of freezing destruction prevention and overheat prevention.

2. Related Art

Recently, technologies have been developed to produce electricity by solar heat as alternative energy of oil or to apply the solar heat to a water heating system. Accordingly, solar water heating systems have been widely proposed and commercialized to produce hot water by using the solar heat.

FIG. 1 shows the configuration of an example of conventional solar water heating systems. A solar water heating system 10 largely includes a solar collector 11, a hot water circulation pipe 12 through which hot water is circulated, a circulation pump C adapted to forcedly circulate the hot water, and a thermal storage tank 14 in which the heated hot water is stored. Residential water is introduced into one side of the hot water circulation pipe 12 and stored in the thermal storage tank 14. The introduced residential water is heated through the solar collector 11 and stored again in the thermal storage tank 14. The residential water stored in the thermal storage tank 14 is discharged through the other side of the hot water circulation pipe 12 and used for households. In this case, the hot water is heated directly in the solar collector 11, thereby enhancing the heat efficiency and being simple in configuration to reduce a possibility of occurrence of troubles. At the time when the temperature drops drastically in winter season, however, the hot water circulation pipe 12 may be frozen and destructed easily, so that the conventional solar water heating system 10 cannot be used in extremely cold regions where the temperature drops below zero, thereby failing to be commercialized.

FIG. 2 shows the configuration of another example of conventional solar water heating systems. A solar water heating system 20 largely includes a solar collector 21, a solar collector circulation pipe 26 connected to the solar collector 21 in such a manner as to allow an operating medium adapted to send the collected solar heat to flow therealong, a hot water circulation pipe 28 through which hot water flows, and a thermal storage tank 22 in which the operating medium and the hot water are heat-exchanged with each other. The thermal storage tank 22 is composed of an outside tank 23 and an inside tank 24 located inside the outside tank 23. The outside tank 23 communicates with the solar collector circulation pipe 26, and the inside tank communicates with the hot water circulation pipe 28. The operating medium flows to the outside tank 23, and residential water flows to the inside tank 24, so that the heat exchange is performed therebetween. In this case, anti-freezing liquid is used as the operating medium so as to prevent the solar collector circulation pipe 26 from being frozen and destructed.

The hot water circulation pipe 28 has a heat wire 29 mounted around the outer periphery thereof. The heat wire 29 is adapted to prevent the hot water circulation pipe 28 from being frozen and destructed in winter season, especially during the time when residential water is not used. If the outside temperature drops below a given temperature in winter season, electric current is applied to the heat wire 29 to heat the hot water circulation pipe 28, thereby preventing the freezing of the hot water circulation pipe 28.

However, the solar water heating system 20 has some problems. That is, the way of preventing the hot water circulation pipe 28 from being frozen and destructed by using the heat wire 29 causes a large quantity of power consumption during the winter season where the temperature drops below zero, and if the heat wire 29 is frequently operated, the heat wire 29 may cut, thereby providing low efficiency and increasing the maintenance cost thereof.

FIG. 3 shows the configuration of yet another example of conventional solar water heating systems. Referring to FIG. 3, a solar water heating system 30 is configured to heat water used for hot water through a heat exchanger 33 where a heating medium (anti-freezing liquid) circulating a solar collector 31 is heat-exchanged with hot water. That is, the solar water heating system 30 includes: the solar collector 31 located outdoors and adapted to absorb solar heat and to heat the water circulated by means of a circulation pump 35, the solar collector 31 being composed of a solar collector inlet pipe 31 a and a solar collector outlet pipe 31 b; the heat exchanger 33 into which the solar collector inlet pipe 31 a and the solar collector outlet pipe 31 b are inserted to perform a heat exchange operation; and a thermal storage tank 37 having a thermal storage inlet pipe 37 a and a thermal storage outlet pipe 37 b whose one ends communicating with the interior of the heat exchanger 33, a thermal storage pump 37 c mounted on the thermal storage outlet pipe 37 b so as to circulate hot water therethrough and to allow the heat exchange operation to be performed in the heat exchanger 33, and a hot water inlet pipe 37 d and a hot water outlet pipe 37 e adapted to supply the heat-exchanged hot water therethrough.

As mentioned above, the heat exchanger 33 is adapted to prevent the water existing in the solar collector inlet pipe 31 a and the solar collector outlet pipe 31 b from freezing in winter season where residential water is not used, thereby avoiding the freezing of the solar collector inlet pipe 31 a and the solar collector outlet pipe 31 b.

According to the conventional solar water heating system 30, the heat exchange operation is not performed with hot water in the thermal storage tank 37, but it is performed with hot water through the heat exchanger 33 mounted separately, so that the temperature of the entrance of the solar collector 31 is raised to cause the heat collection efficiency to be lowered, and further, the quantity of power consumption is substantially increased in winter season where the temperature drops below zero. Moreover, during the heat exchange operation through the heat exchanger 33, heat loss is generated to cause the heat efficiency to be reduced thereby, and further, the heat exchanger 33, the heating medium and the thermal storage pump 37 c should be additionally provided, thereby increasing the whole installation cost of the solar water heating system 30 and the maintenance cost thereof.

SUMMARY OF THE DISCLOSURE

Accordingly, the present invention has been made in view of the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a solar water heating system that is configured to have a plurality of freezing prevention valves operated to allow the residential water existing in an inside tank to flow along a hot water circulation pipe if a temperature of the hot water circulation pipe is below an opening temperature, thereby preventing the hot water circulation pipe from being frozen and destructed, and that is configured to allow the freezing prevention valves and a freezing prevention heater to be operated in accordance with the temperatures of the hot water circulation pipe and a thermal storage tank, thereby preventing the thermal storage tank and a hot water discharge pipe from being frozen and destructed, wherein the solar water heating system can be simple in configuration, have a substantially high heat efficiency, and achieve overheat prevention.

To accomplish the above object, according to the present invention, there is provided a solar water heating system including: a solar collector to which solar heat is collected; a solar collector circulation pipe connected to the solar collector and adapted to circulate an operating medium on which the solar heat collected by the solar collector is accumulated therealong;

a thermal storage tank in which the operating medium and the water used for living are heat-exchanged with each other; a hot water circulation pipe communicating with the thermal storage tank, to which the water is supplied; a freezing prevention valve located on one side of the hot water circulation pipe and adapted to be selectively open and closed to allow the water in the thermal storage tank to selectively flow along the hot water circulation pipe; and a controller adapted to control the operation of the freezing prevention valve in accordance with the variation of at least one or more of a temperature T1 of a given portion of the hot water circulation pipe and a temperature T2 of the water in the thermal storage tank, thereby preventing the hot water circulation pipe from being frozen and destructed.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which:

FIG. 1 shows the configuration of an example of conventional solar water heating systems;

FIG. 2 shows the configuration of another example of conventional solar water heating systems;

FIG. 3 shows the configuration of yet another example of conventional solar water heating systems;

FIG. 4 shows the configuration of a solar water heating system according to a first embodiment of the present invention;

FIGS. 5 and 6 show the configuration of a solar water heating system according to a second embodiment of the present invention, wherein the flows of hot water and operating medium are illustrated;

FIGS. 7 and 8 show the configuration of a solar water heating system according to a third embodiment of the present invention, wherein the operation of the valve and the flows of hot water for freezing destruction prevention are illustrated;

FIG. 9 shows the configuration of a solar water heating system according to a fourth embodiment of the present invention;

FIGS. 10 and 11 show the configuration of a solar water heating system according to the fourth embodiment of the present invention, wherein the flows of hot water are illustrated;

FIG. 12 shows the configuration of a solar water heating system according to a fifth embodiment of the present invention;

FIG. 13 shows the configuration of a solar water heating system according to the fifth embodiment of the present invention, wherein the flows of hot water and operating medium are illustrated;

FIG. 14 shows the configuration of a solar water heating system according to the fifth embodiment of the present invention, wherein the operation of the valve and the flows of hot water for freezing destruction prevention are illustrated;

FIG. 15 shows the configuration of a solar water heating system according to a sixth embodiment of the present invention;

FIG. 16 shows the configuration of a solar water heating system according to a seventh embodiment of the present invention;

FIG. 17 shows the configuration of a solar water heating system according to an eighth embodiment of the present invention;

FIG. 18 shows the flows of hot water when the solar water heating system of FIG. 17 is operated;

FIG. 19 shows the flows of hot water when the solar water heating system of FIG. 17 is operated at night during winter season; and

FIG. 20 shows the flows of hot water when the solar water heating system of FIG. 17 is operated during summer season.

DETAILED DESCRIPTION OF THE DISCLOSURE

Hereinafter, an explanation on a solar water heating system according to the preferred embodiments of the present invention will be in detail given with reference to the attached drawings.

FIG. 4 shows the configuration of a solar water heating system according to a first embodiment of the present invention.

A solar water heating system 100 according to the first embodiment of the present invention includes a solar collector 110 adapted to effectively collect solar heat thereto, and in this case, various types of solar collectors such as vacuum tube solar collectors, flat plate solar collectors and the like can be used as the solar collector 110.

The solar collector 110 is connected to a solar collector circulation pipe 115. The solar collector circulation pipe 115 is a closed pipe not connected to the outside, while being located partially inside the solar collector 110. The solar collector circulation pipe 115 serves as a passage through which an operating medium as will be discussed later flows, and in this case, the operating medium flows along the solar collector circulation pipe 115 and absorbs the solar heat collected through the solar collector 110 at the time of passing the portion of the solar collector circulation pipe 115 located inside the solar collector 110, so that the absorbed solar heat is sent to residential water as will be explained later.

Even though not shown, desirably, the portion of the solar collector circulation pipe 115 located inside the solar collector 110 is expanded to the interior of the solar collector 110 so as to send the heat collected to the solar collector 110 to the operating medium to the maximum degree. Further, the solar collector circulation pipe 115 may include a heat insulation material provided along the outer periphery thereof so as to prevent the solar heat from being sent to the outside. Even though not shown, also, the solar collector circulation pipe 115 may include a circulation pump adapted to gently circulate the operating medium therealong.

The operating medium (not shown) flows along the solar collector circulation pipe 115. The operating medium flows along the solar collector circulation pipe 115 to send the heat collected through the solar collector 110. Anti-freezing liquid, which is generally not frozen at a relatively low temperature, is used as the operating medium.

The solar water heating system 100 further includes a hot water circulation pipe 120 serving as a passage through which residential water, that is, tap water supplied from a water supply system is moved, and in this case, the water is heated while flowing along the hot water circulation pipe 120. In more detail, the residential water flows along the hot water circulation pipe 120 and has a heat exchange (conduction) operation with the operating medium, thereby being heated.

The hot water circulation pipe 120 is open at both sides thereof. In this case, the hot water circulation pipe 120 has one side connected to the water supply system supplying the residential water to introduce the residential water thereinto and the other side through which the residential water (hot water) whose temperature is raised after passing through the hot water circulation pipe 120 is discharged and used for living.

The hot water circulation pipe 120 is composed of a hot water intake pipe 123 adapted to introduce water into a thermal storage tank 130 as will be discussed later and a hot water discharge pipe 125 adapted to discharge the water of the thermal storage tank 130 therefrom.

The hot water discharge pipe 125 is disposed at a relatively higher location than the hot water intake pipe 123. This is because the temperature of the hot water located at a relatively high position is higher than that located at a relatively low position through the stratification effect of the hot water stored in an inside tank 130 a, and thus, the hot water having the relatively high temperature is used. Since the hot water intake pipe 123 is connected to the water supply system, no separate circulation pump is needed.

As shown in FIG. 4, a hot water outflow pipe 125′ is disposed at one side of the hot water discharge pipe 125. The hot water outflow pipe 125′ communicates with the hot water discharge pipe 125 and thus serves as a passage through which the water existing in the thermal storage tank 130 is discharged through the hot water discharge pipe 125. Even though not shown, a heavy water tank may be connected to the hot water outflow pipe 125′. The heavy water tank is adapted to store the residential water and hot water discharged through the hot water outflow pipe 125′ thereinto and to reuse them. The hot water stored in the heavy water tank may be used for bathrooms.

The hot water outflow pipe 125′ has a freezing prevention valve 125″ disposed thereon. The freezing prevention valve 125″ serves to selectively open and close the hot water outflow pipe 125′. In more detail, if a temperature T1 of a portion of the hot water intake pipe 123 is lowered below a given temperature, the freezing prevention valve 125″ is open to permit the water stored in the inside tank 130 a having a relatively high temperature to flow along the hot water intake pipe 123. The water flowing along the hot water intake pipe 123 is discharged to the hot water discharge pipe 125 by means of its own self weight and stored again in the heavy water tank (not shown) for reusing.

According to the properties of water, the volume of water in a solid state (ice) is larger than that in a liquid state. Water is always charged in the hot water circulation pipe 120, and during the time (night) when water is not used, water does not flow along the hot water circulation pipe 120, especially the hot water discharge pipe 125 and stays therein.

If the residential water is frozen due to a drop of temperature, it is expanded in volume to cause the hot water circulation pipe 120 to be frozen and destructed.

When the temperature of the hot water intake pipe 123 is lowered below the given temperature, accordingly, the temperature in the hot water circulation pipe 120, more particularly, in the hot water discharge pipe 125 is increased through the water stored in the inside tank 130 a having a relatively high temperature, thereby preventing the hot water circulation pipe 120 from being frozen and destructed.

Since the portion of the hot water discharge pipe 125 exposed to external air has a relatively low temperature, at this time, the temperature of the exposed portion of the hot water discharge pipe 125 should be preferably measured.

The degree of opening of the freezing prevention valve 125″ is changed in accordance with the variation of the temperature of the hot water intake pipe 123. That is, the lower the temperature of the hot water intake pipe 123 is, the larger the degree of opening of the freezing prevention valve 125″ is, so that a large amount of hot water flows to increase the temperature of the hot water circulation pipe 120.

If the temperature T1 of the portion of the hot water intake pipe 123 is raised above a given temperature, the freezing prevention valve 125″ is closed again.

The solar water heating system 100 further includes the thermal storage tank 130. The thermal storage tank 130 is the space where the heat exchange between the operating medium and the residential water is performed. The thermal storage tank 130 is desirably surrounded with a heat insulation material so as to enhance the heat exchange efficiency and to prevent heat from emitting to the outside. The thermal storage tank 130 is largely composed of the inside tank 130 a and an outside tank 130 b adapted to surround the inside tank 130 a. As shown in FIG. 4, the inside tank 130 a and the outside tank 130 b do not communicate with each other and have a given space therebetween to flow the operating medium therealong.

The outside tank 130 b communicates with the solar collector circulation pipe 115, and the inside tank 130 a with the hot water circulation pipe 120. The operating medium flowing along the solar collector circulation pipe 115 is introduced into the outside tank 130 b and flows therealong to send the heat to the inside tank 130 a, and the heat sent to the inside tank 130 a increases the temperature of the residential water, thereby making hot water. The outside tank 130 b and the inside tank 130 a are desirably made of a material having a relatively high thermal conductivity like copper so as to enhance their heat exchange efficiency. Further, the inside tank 130 a has a substantially large range of surface area contacted with the operating medium existing in the outside tank 130 b so as to perform gentle heat transmission.

The solar water heating system 100 further includes a freezing prevention heater 135. The freezing prevention heater 135 serves to control a temperature T2 of the inside tank 130 a.

That is, the freezing prevention heater 135 applies heat in accordance with the variation of the temperature T2 of the inside tank 130 a, thereby adjusting the temperature T2. The freezing prevention heater 135 has a heat wire 135′ mounted thereon, and a portion of the heat wire 135′ is located in the inside tank 130 a.

The freezing prevention heater 135 is connected to a controller C as will be discussed later, and if the temperature T2 of the inside tank 130 a is lowered below a given temperature, electric current flows along the heat wire 135′ to generate heat from the heat wire 135′. Through the heat generated from the heat wire 135′, accordingly, the temperature T2 of the inside tank 130 a is maintained at the given temperature to prevent the inside tank 130 a from being frozen and destructed. Further, the temperature of the hot water in the inside tank 130 a is raised to increase the temperature of the hot water discharged through the hot water circulation pipe 120, thereby preventing the hot water circulation pipe 120 from being frozen and destructed.

The freezing prevention valve 125″ and the freezing prevention heater 135 are connected to the controller C. Further, the controller C is connected to sensors S and S′ adapted to measure the temperatures of the hot water intake pipe 123 and the inside tank 130 a. The controller C measures the temperatures of the hot water intake pipe 123 and the inside tank 130 a to adjust the opening/closing of the freezing prevention valve 125″ and to control the operation of the freezing prevention heater 135. The sensor S is mounted on the portion exposed to the external air of the hot water intake pipe 123 whose temperature is lowest thereon.

Hereinafter, a process of controlling the freezing prevention valve 125″ and the freezing prevention heater 135 by means of the controller C in the solar water heating system 100 according to the present invention will be explained. The explanation is given in accordance with second and third embodiments of the present invention, and the second and third embodiments have the same configuration as in the solar water heating system 100 and have different processes of controlling the freezing prevention valve 125″ and the freezing prevention heater 135 in accordance with the variations of the conditions of the temperatures T1 and T2. First, the second embodiment of the present invention will be discussed.

FIGS. 5 and 6 show the configuration of the solar water heating system according to the second embodiment of the present invention, wherein the flows of hot water and operating medium are illustrated.

According to the second embodiment of the present invention, if the temperature T1 of the hot water circulation pipe 120, especially, the hot water discharge pipe 125 is below Ta (wherein 1° C.≦Ta≦6° C., more preferably, Ta=4° C.), the freezing prevention valve 125″ is open by means of the controller C. At this time, the range of the Ta is set in accordance with seasons and regions, and when the changes in the temperature of the tap water by seasons are considered, 4° C. is a mean value. Accordingly, the Ta is desirably set to 4° C.

If the freezing prevention valve 125″ is open, the water existing in the thermal storage tank 130, especially, in the inside tank 130 a of the thermal storage tank 130 is passed through the hot water discharge pipe 125 and discharged to the hot water outflow pipe 125′. The water existing in the thermal storage tank 130 has a relatively high temperature, and thus, the water is heat-exchanged while passing through the hot water discharge pipe 125, thereby increasing the temperature of the hot water discharge pipe 125.

Through the opening of the freezing prevention valve 125″, the temperature T1 of the hot water discharge pipe 125 is raised, and if the temperature T1 of the hot water discharge pipe 125 is above Tc (wherein 9° C≦Tc≦11° C., more preferably, Tc=10° C.), the freezing prevention valve 125″ is closed by means of the controller C, as shown in FIG. 5. Like the Ta, at this time, the range of the Tc is set in accordance with seasons and regions, and when the annual temperature of the tap water is considered, the Tc is most desirably set to 10° C. If the Tc is below 10° C., the operation of the freezing prevention valve 125″ is frequently performed to decrease the whole efficiency of the system. If the freezing prevention valve 125″ is closed, the supply of the water from the interior of the thermal storage tank 130 stops.

As mentioned above, if the freezing prevention valve 125″ is controlled by means of the controller C, the temperature T1 of the hot water outflow pipe 125′ is maintained to the condition 4° C<T1<10° C. (most desirably, in case where Ta=4° C. and Tc=10° C.). Since the average temperature of the tap water is between 4° C. and 10° C., the temperature T1 is controlled and maintained in the above condition.

In case where Ta=4° C. and Tc=10° C., most desirably, the temperature T1 of the hot water discharge pipe 125 becomes the maximum 10° C., so that the temperature T2 of the thermal storage tank 130 should be kept above at least 10° C. If the temperature T2 of the thermal storage tank 130 is below 10° C., accordingly, the freezing prevention heater 135 is operated by means of the controller C. If the freezing prevention heater 135 is operated, the temperature T2 of the thermal storage tank 130 is raised. If the temperature T2 of the thermal storage tank 130 is above the given temperature, desirably above 12° C., through the operation of the freezing prevention heater 135, the operation of the freezing prevention heater 135 stops. Like this, the freezing prevention valve 125″ and the freezing prevention heater 135 are controlled by means of the controller C to prevent the hot water circulation pipe 120 from being frozen and destructed during the winter season and to reduce the maintenance cost of the solar water heating system 100, without having any separate heater.

FIGS. 7 and 8 show the configuration of a solar water heating system according to the third embodiment of the present invention, wherein the operation of the valve and the flows of hot water for freezing destruction prevention are illustrated.

If the solar water heating system according to the second embodiment of the present invention is carried out in extremely cold regions, the time for operating the freezing prevention heater 135 is extended, and therefore, the solar water heating system according to the second embodiment of the present invention is not adequate for the use in the extremely cold regions. Accordingly, the solar water heating system according to the third embodiment of the present invention, which is adequate for the use in the extremely cold regions, will be explained.

According to the third embodiment of the present invention, if the temperature T1 of a portion of the hot water discharge pipe 125 is below Ta (wherein 1° C.≦Ta≦6° C., more preferably, Ta=4° C.), the freezing prevention valve 125″ is open by means of the controller C. If the freezing prevention valve 125″ is open, the water existing in the thermal storage tank 130, especially, in the inside tank 130 a of the thermal storage tank 130 is passed through the hot water discharge pipe 125 and discharged to the hot water outflow pipe 125′. The water existing in the thermal storage tank 130 has a relatively high temperature, and thus, the water is heat-exchanged while passing through the hot water discharge pipe 125, thereby increasing the temperature of the hot water discharge pipe 125.

After that, if the temperature T1 of the hot water discharge pipe 125 satisfies the following conditions (1) and (2), the freezing prevention valve 125″ is closed by means of the controller C.

T2>Tb, T1>Tc  Condition (1)

T2≦Tb, T1>T2−dT  Condition (2)

*11° C<Tb≦14° C., 9° C≦Tc≦11° C., 1° C≦dT≦3° C.

In more detail, if the temperature T2 of the water in the thermal storage tank 130 is above Tb (wherein 11° C.≦Tb≦14° C.) and the temperature T1 of the hot water discharge pipe 125 is above Tc (wherein 9° C≦Tc≦11° C.), the freezing prevention valve 125″ is closed, and further, if the temperature T2 of the water in the thermal storage tank 130 is below Tb (wherein 11° C<Tb≦14° C.) and the temperature T1 of the hot water discharge pipe 125 is above T2−dT (wherein 1° C≦dT≦3° C.), the freezing prevention valve 125″ is closed.

In the third embodiment of the present invention, the conditions of both of the temperature T1 of the hot water discharge pipe 125 and the temperature T2 of the water in the thermal storage tank 130 are adjusted together. In case of the extremely cold regions, a temperature is too low to maintain the temperature T2 of the water in the thermal storage tank 130 to the given temperature, and further, if the freezing prevention heater is used, the quantity of electricity consumed is increased. Accordingly, the freezing prevention valve 125″ is controlled by means of the controller C in accordance with the temperature T2 of the water in the thermal storage tank 130.

Most preferably, the Ta is 4° C., Tb is 12° C., Tc is 10° C., and dT is 2° C. In this case, the dT has 2° C. as a minimum value for preventing the malfunction of the controller C, and the Tb has 12° C. as a value obtained by the dT and Tc values. The Ta and Tc are the same values as mentioned in the second embodiment, and therefore, their explanation will be avoided.

If the condition where Ta is 4° C., Tb is 12° C., Tc is 10° C., and dT is 2° C. is satisfied, the temperature T2 of the water in the thermal storage tank 130 should be maintained above 4° C. as a reference temperature capable of opening the freezing prevention valve 125″ and at the same time it should be maintained above 6° C. to satisfy the above condition (2) (In the condition (2), since T1>T2−2° C., T1 should be maintained above at least 6° C.). If the temperature T2 of the water in the thermal storage tank 130 is below 6° C., accordingly, the freezing prevention heater 135 is operated by means of the controller C to increase the temperature T2 of the water in the thermal storage tank 130, and contrarily, if the temperature T2 of the water in the thermal storage tank 130 is above 8° C., the operation of the freezing prevention heater 135 stops by means of the controller C.

According to the third embodiment of the present invention, the freezing prevention valve 125″ and the freezing prevention heater 135 are controlled by means of the controller C in consideration of the temperature T1 of the hot water discharge pipe 125 and the temperature T2 of the water in the thermal storage tank 130, so that there is no need for maintaining the temperature T2 of the water in the thermal storage tank 130 to the given temperature or more even in the extremely cold regions, and thus, the solar water heating system 100 has good efficiency and low maintenance cost.

Next, an explanation on a solar water heating system according to a fourth embodiment of the present invention will be given.

FIG. 9 shows the configuration of the solar water heating system according to the fourth embodiment of the present invention, and FIGS. 10 and 11 show the configuration of the solar water heating system according to the fourth embodiment of the present invention, wherein the flows of hot water are illustrated.

According to the fourth embodiment of the present invention, the configuration is the same as those in the first to third embodiments of the present invention, except that a connection pipe 227, a check valve cv, and a circulation pump P are additionally disposed therein, and therefore, they will be in detail explained.

The connection pipe 227 is disposed between a hot water intake pipe 223 and a hot water discharge pipe 225 and serves to allow the hot water intake pipe 223 and the hot water discharge pipe 225 to communicate with each other, so that the water in a thermal storage tank 230 is circulated along the hot water intake pipe 223 and the hot water discharge pipe 225 by means of the connection pipe 227. That is, the water of the thermal storage tank 230 discharged through the hot water discharge pipe 225 is passed through the connection pipe 227 and introduced into the hot water intake pipe 223.

The connection pipe 227 has the check valve cv mounted thereon. The check valve cv serves to allow the connection pipe 227 to selectively communicate with the hot water intake pipe 223 and the hot water discharge pipe 225, thereby permitting one way flow through the connection pipe 227. In more detail, either the flow of the water from the hot water intake pipe 223 toward the hot water discharge pipe 225 or the flow of the water from the hot water discharge pipe 225 toward the hot water intake pipe 223 is permitted by means of the opening/closing of the check valve cv. For example, the process of opening the check valve cv in case of the flow of the water from the hot water discharge pipe 225 toward the hot water intake pipe 223 will be discussed in this embodiment.

The connection pipe 227 has the circulation pump P mounted thereon. The circulation pump P serves to provide power capable of allowing water to flow along the connection pipe 227. For example, the process of providing power by means of the circulation pump P in case of the flow of the water from the hot water discharge pipe 225 toward the hot water intake pipe 223 will be discussed in this embodiment.

According to the fourth embodiment of the present invention, if the temperature T1 of a portion of the hot water discharge pipe 225 is below Ta (wherein 1° C≦Ta≦6° C., more preferably, Ta=2° C.), the circulation pump P is operated by means of the controller C. If the circulation pump P is operated, the water existing in the thermal storage tank 230, especially, in an inside tank 230 a of the thermal storage tank 230 is passed through the hot water discharge pipe 225 and the connection pipe 227 and introduced into the hot water intake pipe 223. Next, the water is introduced again into the inside tank 230 a of the thermal storage tank 230. The water existing in the inside tank 230 a has a relatively high temperature, thereby increasing the temperatures of the hot water discharge pipe 225 and the hot water intake pipe 223. If the circulation pump P is operated, the check valve cv is open to cause the water to flow along the connection pipe 227.

After that, if the temperature T1 of the hot water discharge pipe 225 satisfies the following conditions (1) and (2), the operation of the circulation pump P stops by means of the controller C.

T2>Tb, T1>Tc  Condition (1)

T2≦Tb, T1>T2−dT  Condition (2)

*11° C<Tb≦14° C., 9° C≦Tc≦11° C., 1° C≦dT≦3° C.

In more detail, if the temperature T2 of the water in the thermal storage tank 230 is above Tb (wherein 11° C<Tb≦14° C.) and the temperature T1 of the hot water discharge pipe 225 is above Tc (wherein 9° C≦Tc≦11° C.), the operation of the circulation pump P stops, and further, if the temperature T2 of the water in the thermal storage tank 230 is below Tb (wherein 11° C<Tb≦14° C.) and the temperature T1 of the hot water discharge pipe 225 is above T2−dT (wherein 1° C≦dT≦3° C.), the operation of the circulation pump P stops.

If the operation of the circulation pump P stops, the check valve cv is closed, so that the water does not flow backwardly through the connection pipe 227.

In the fourth embodiment of the present invention, the conditions of both of the temperature T1 of the hot water discharge pipe 225 and the temperature T2 of the water in the thermal storage tank 230 are adjusted together in the same manner as the third embodiment. At this time, since the quantity of electricity for the operation of the circulation pump P is smaller than that for activation of the heat wire, the efficiency of the solar water heating system can be improved, and since the tap water flows in winter season, the freezing prevention effect can be obtained, thereby having no need for further heating the thermal storage tank 230 at a relatively low temperature. A separate freezing prevention heater 235 may be provided, and at this time, the operating conditions of the freezing prevention heater 235 are the same as those in the third embodiment of the present invention. Accordingly, the explanation on them will be avoided for the brevity of the description.

Most preferably, the Ta is 2° C., Tb is 12° C., Tc is 10° C., and dT is 2° C. At this time, the set values are the same as those in the third embodiment of the present invention, and accordingly, the explanation on them will be avoided for the brevity of the description.

According to the fourth embodiment of the present invention, the water of the thermal storage tank 230 is circulated through the hot water discharge pipe 225 and the hot water intake pipe 223 to prevent the solar water heating system 200 from being frozen and destructed even at a relatively low temperature, thereby improving the operating efficiency of the solar water heating system 200 and reducing the maintenance cost thereof.

FIG. 12 shows the configuration of a solar water heating system according to a fifth embodiment of the present invention.

A solar water heating system 300 according to the fifth embodiment of the present invention includes a solar collector 310 adapted to effectively collect solar heat thereto, and in this case, various types of solar collectors such as vacuum tube solar collectors, flat plate solar collectors and the like can be used as the solar collector 310.

The solar collector 310 is connected to a solar collector circulation pipe 315. The solar collector circulation pipe 315 is a closed pipe not connected to the outside, while being located partially inside the solar collector 310. The solar collector circulation pipe 315 serves as a passage through which an operating medium as will be discussed later flows, and in this case, the operating medium flows along the solar collector circulation pipe 315 and absorbs the solar heat collected through the solar collector 310 at the time of passing the portion of the solar collector circulation pipe 315 located inside the solar collector 310, so that the absorbed solar heat is sent to residential water as will be explained later.

Even though not shown, desirably, the portion of the solar collector circulation pipe 315 located inside the solar collector 310 is expanded to the interior of the solar collector 310 so as to send the heat collected to the solar collector 310 to the operating medium to the maximum degree. Further, the solar collector circulation pipe 315 may include a heat insulation material provided along the outer periphery thereof so as to prevent the solar heat from being sent to the outside. Even though not shown, also, the solar collector circulation pipe 315 may include a circulation pump adapted to gently circulate the operating medium therealong.

The operating medium (not shown) flows along the solar collector circulation pipe 315. The operating medium flows along the solar collector circulation pipe 315 to send the heat collected through the solar collector 310. Anti-freezing liquid, which is generally not frozen at a relatively low temperature, is used as the operating medium.

The solar water heating system 300 further includes a hot water circulation pipe 320 serving as a passage through which residential water, that is, tap water supplied from a water supply system is moved, and in this case, the water is heated while flowing along the hot water circulation pipe 320. In more detail, the residential water flows along the hot water circulation pipe 320 and has the heat exchange (conduction) with the operating medium, thereby being heated. In the preferred embodiment, the heated state of the residential water is called hot water.

The hot water circulation pipe 320 is open at both sides thereof. In this case, the hot water circulation pipe 120 has one side connected to the water supply system supplying the residential water to introduce the residential water thereinto and the other side through which the residential water (hot water) whose temperature is raised after passing through the hot water circulation pipe 320 is discharged and used for living. The hot water circulation pipe 320 is composed of a hot water intake pipe 323 into which the residential water is introduced from a thermal storage tank 330 as will be discussed later and a hot water discharge pipe 325 through which the hot water is discharged from the thermal storage tank 330.

The hot water discharge pipe 325 is disposed at a relatively higher location than the hot water intake pipe 323. This is because the temperature of the hot water located at a relatively high position is higher than that located at a relatively low position through the stratification effect of the hot water stored in an inside tank 330 a, and thus, the hot water having the relatively high temperature is used. Since the hot water intake pipe 323 is connected to the water supply system, no separate circulation pump is needed.

First and second outflow pipes 323′ and 325′ are disposed on the hot water intake pipe 323 and the hot water discharge pipe 325. The first and second outflow pipes 323′ and 325′ communicate with the hot water intake pipe 323 and the hot water discharge pipe 325 and thus serve as passages through which the residential water and hot water existing in the inside tank 330 a are discharged through the hot water intake pipe 323 and the hot water discharge pipe 325. Even though not shown, a heavy water tank may be connected to the first and second outflow pipes 323′ and 325′, respectively. The heavy water tank is adapted to store the residential water and hot water discharged through the first and second outflow pipes 323′ and 325′ thereinto and to reuse them. The hot water stored in the heavy water tank may be used for bathrooms.

The first and second outflow pipes 323′ and 325′ have first and second freezing prevention valve 323″ and 325″ disposed thereon. The first and second freezing prevention valve 323″ and 325″ serve to selectively open and close the first and second outflow pipes 323′ and 325′. In more detail, if a temperature T1 of the hot water intake pipe 323 is lowered to a given temperature, desirably, below 2° C., the first and second freezing prevention valve 323″ and 325″ are open to permit the hot water stored in the inside tank 330 a having a relatively high temperature to flow along the hot water intake pipe 323 and the hot water discharge pipe 325 by means of its own self weight. The temperature where the first and second freezing prevention valve 323″ and 325″ are open is called an opening temperature.

The hot water intake pipe 323 is connected to the water supply system for supplying the residential water thereto, and at this time, the supply of the residential water stops through the closing of a third freezing prevention valve 327 as will be discussed later. That is, when the first freezing prevention valve 323″ is open, the third freezing prevention valve 327 is closed to stop the introduction of the residential water and at the same time the hot water in the inside tank 330 a flows backwardly to the hot water intake pipe 323 and introduced into the heavy water tank through the first outflow pipe 323′. Further, when the second freezing prevention valve 325″ is open, the hot water is passed through the hot water discharge pipe 325 and introduced into the heavy water tank through the second outflow pipe 325′.

According to the properties of water, the volume of water in a solid state (ice) is larger than that in a liquid state. Water is always charged in the hot water circulation pipe 320, and during the time (night) when water is not used, water does not flow along the hot water circulation pipe 320, especially the hot water discharge pipe 325 and stays therein. If the residential water is frozen due to a drop of temperature, it is expanded in volume to cause the hot water circulation pipe 320 to be frozen and destructed.

When the temperature of the hot water intake pipe 323 is lowered below the opening temperature, accordingly, the hot water stored in the inside tank 330 a having a relatively high temperature is allowed to flow through the hot water circulation pipe 320, so that the temperature in the hot water circulation pipe 320 is increased to prevent the hot water circulation pipe 320 from being frozen and destructed. In the embodiment, desirably, the opening temperature is set to 2° C. to increase the temperature of water before the water is frozen, and therefore, when the temperature of the hot water intake pipe 323 reaches 2° C., the hot water flows.

At this time, measuring the temperature of the hot water intake pipe 323 of the hot water circulation pipe 320 is needed because the temperature of the hot water intake pipe 323 into which the residential water having a relatively low temperature is introduced is lower than that of the hot water discharge pipe 325 from which the hot water having a relatively high temperature is discharged. Further, since the portion of the hot water intake pipe 323 exposed to external air has a relatively low temperature, the temperature of the exposed portion of the hot water intake pipe 323 should be preferably measured.

The hot water intake pipe 323 of the hot water circulation pipe 320 has the third freezing prevention valve 327 mounted thereon. The third freezing prevention valve 327 is closed when the first freezing prevention valve 323″ is open in accordance with the variation of the temperature of the hot water circulation pipe 320, thereby preventing the residential water from being supplied to the hot water intake pipe 323. That is, the third freezing prevention valve 327 is open in normal cases, but if the first and second freezing prevention valve 323″ and 325″ are open, the third freezing prevention valve 327 is closed to stop the supply of the residential water.

The degree of opening of the first and second freezing prevention valve 323″ and 325″ is changed in accordance with the variation of the temperature of the hot water intake pipe 323. That is, the lower the temperature of the hot water intake pipe 323 is, the larger the degree of opening of the first and second freezing prevention valve 323″ and 325″ is, so that a large amount of hot water flows to increase the temperature of the hot water circulation pipe 320.

If the temperature of the hot water intake pipe 323 is raised above the closing temperature, the first and second freezing prevention valve 323″ and 325″ are closed again, and the third freezing prevention valve 327 is open to permit the residential water to be introduced into the hot water intake pipe 323 and the hot water discharge pipe 325. In the preferred embodiment, if the temperature of the hot water intake pipe 323 is above 10° C., the freezing of the hot water circulation pipe 320 is prevented, and therefore, the closing temperature is set to 10° C. The opening/closing and degrees of opening of the first to third freezing prevention valves 323″, 325″ and 327 are controlled by means of a controller 340 as will be discussed later.

The solar water heating system 300 further includes the thermal storage tank 330. The thermal storage tank 330 is the space where the heat exchange between the operating medium and the residential water is performed. The thermal storage tank 330 is desirably surrounded with a heat insulation material so as to enhance the heat exchange efficiency and to prevent heat from emitting to the outside. The thermal storage tank 330 is largely composed of the inside tank 330 a and an outside tank 330 b adapted to surround the inside tank 330 a. As shown in FIG. 12, the inside tank 330 a and the outside tank 330 b do not communicate with each other and have a given space therebetween to flow the operating medium therealong.

The outside tank 330 b communicates with the solar collector circulation pipe 315, and the inside tank 330 a with the hot water circulation pipe 320. The operating medium flowing along the solar collector circulation pipe 315 is introduced into the outside tank 330 b and flows therealong to send the heat to the inside tank 330 a, and the heat sent to the inside tank 330 a increases the temperature of the residential water, thereby making hot water. The outside tank 330 b and the inside tank 330 a are desirably made of a material having a relatively high thermal conductivity like copper so as to enhance their heat exchange efficiency. Further, the inside tank 330 a has a substantially large range of surface area contacted with the operating medium existing in the outside tank 330 b so as to perform gentle heat transmission.

The solar water heating system 300 further includes a freezing prevention heater 335. The freezing prevention heater 335 serves to apply heat to the inside tank 330 a to raise the inside tank 330 a to a given temperature if the temperature of the inside tank 330 a is below the opening temperature, that is, 2° C. The freezing prevention heater 335 has a heat wire 335′ mounted thereon, and a portion of the heat wire 335′ is located in the inside tank 330 a. The freezing prevention heater 335 is connected to the controller 340, and if the temperature of the inside tank 330 a is lowered below the given temperature, electric current flows along the heat wire 335′ to generate heat from the heat wire 335′. Through the heat generated from the heat wire 335′, accordingly, the temperature of the inside tank 330 a is maintained at the given temperature to prevent the inside tank 330 a from being frozen and destructed. Further, the temperature of the hot water in the inside tank 330 a is raised to increase the temperature of the hot water discharged through the hot water circulation pipe 320, thereby preventing the hot water circulation pipe 320 from being frozen and destructed.

The operation of the freezing prevention heater 335 stops if the temperature of the inside tank 330 a is raised above the closing temperature, that is, 10° C.

The first to third freezing prevention valves 323″, 325″ and 327 and the freezing prevention heater 335 are connected to the controller 340. Further, the controller 340 is connected to sensors S and S′ adapted to measure the temperatures of the hot water intake pipe 323 and the inside tank 330 a. The controller 340 measures the temperatures of the hot water intake pipe 323 and the inside tank 330 a to adjust the opening/closing of the first to third freezing prevention valves 323″, 325″ and 327 and to control the operation of the freezing prevention heater 335. The sensor S is mounted on the portion exposed to the external air of the hot water intake pipe 323 whose temperature is lowest thereon.

Hereinafter, an operating process of the solar water heating system 300 according to the fifth embodiment of the present invention will be in detail explained.

FIG. 13 shows the configuration of a solar water heating system according to the fifth embodiment of the present invention, wherein the flows of hot water and operating medium are illustrated, and FIG. 14 shows the configuration of a solar water heating system according to the fifth embodiment of the present invention, wherein the operation of the valve and the flows of hot water for freezing destruction prevention are illustrated.

First, solar heat is collected to the solar collector 310, and the temperature of the solar collector 310 is raised. The solar heat collected to the solar collector 310 is transmitted to the operating medium flowing along the solar collector circulation pipe 315 connected to the solar collector 310. The operating medium heated through the solar collector 310 is introduced into the thermal storage tank 330, especially into the outside tank 330 b. On the other hand, the residential water introduced into the hot water circulation pipe 320 from the water supply system is sent to the inside tank 330 a through the hot water intake pipe 323.

In the thermal storage tank 330, the operating medium having the relatively high temperature sent to the outside tank 330 b is heat-exchanged through conduction with the residential water having the relatively low temperature introduced into the inside tank 330 a, and thus, the residential water becomes hot water. The hot water of the inside tank 330 a is discharged through the hot water discharge pipe 325 and used in households. Further, the operating medium passed through the outside tank 330 b sends heat to the residential water and thus has a relatively low temperature. Next, the operating medium flows along the solar collector circulation pipe 315 and thus has a relatively high temperature after being passed through the solar collector 310. Through the repetition of the above-mentioned processes in the solar water heating system 300, the residential water becomes hot water.

Next, an operation of preventing the freezing of the solar water heating system 300 will be explained.

The controller 340 is connected to the sensors S and S′ disposed on the inside tank 330 a and the hot water intake pipe 323 to receive the temperatures of the inside tank 330 a and the hot water intake pipe 323. If the freezing prevention heater 335 is provided in the solar water heating system 300, it is operated by means of the controller 340 at the time when the temperature of the inside tank 330 a is lowered below the opening temperature (2° C.), thereby increasing the temperature of the hot water of the inside tank 330 a and preventing the thermal storage tank 330 from being frozen and destructed. As the temperature of the hot water of the inside tank 330 a is increased, a quantity of heat exchange with the outside tank 330 b is reduced, and the operating medium discharged from the outside tank 330 b is maintained to a relatively high temperature.

On the other hand, if the temperature of the hot water intake pipe 323 is lowered below the opening temperature, the first and second freezing prevention valves 323″ and 325″ are open and the third freezing prevention valve 327 is closed by means of the controller 340. The residential water stored in the inside tank 330 a is the hot water having a relatively high temperature that is heat-exchanged with the operating medium in the thermal storage tank 330. The hot water in the inside tank 330 a is passed through the first and second outflow pipes 323′ and 325′ by means of the opening of the first and second freezing prevention valves 323″ and 325″ and discharged and stored to the heavy water tank. In the discharging process, the temperature of the hot water circulation pipe 320 is raised. At this time, the lower the temperature of the hot water intake pipe 323 is below the opening temperature, the larger the degrees of opening of the first and second freezing prevention valves 323″ and 325″ are.

Through the closing of the third freezing prevention valve 327, the supply of the residential water to the hot water intake pipe 323 stops, and the quantity of residential water stored in the inside tank 330 a is reduced. As mentioned above, the quantity of hot water existing in the inside tank 330 a is decreased to prevent the inside tank 330 a from being frozen and destructed due to the extremely cold weather. Since the first and second outflow pipes 323′ and 325′ are connected to the heavy water tank, the hot water discharged from the inside tank 330 a to the outside is reused as heavy water.

If the temperature of the hot water intake pipe 323 is raised above the closing temperature (10° C.), the first and second freezing prevention valves 323″ and 325″ are closed and the third freezing prevention valve 327 is open by means of the controller 340.

At this time, the residential water is introduced through the hot water intake pipe 323, and the introduced residential water is introduced again into the inside tank 330 a. Like this, in the state where the hot water circulation pipe 320 may be frozen and destructed through the drop of the temperature, if the temperature of the hot water intake pipe 323 is lowered below the opening temperature, the residential water of the inside tank 330 a having a relatively high temperature flows backwardly through the first to third freezing prevention valves 323″, 325″ and 327 to avoid the state where the temperature of the hot water intake pipe 323 is lowered below the opening temperature, thereby preventing the solar water heating system 300 from being frozen and destructed.

FIG. 15 shows the configuration of a solar water heating system according to a sixth embodiment of the present invention.

According to the sixth embodiment of the present invention, the solar collector 310, the solar collector circulation pipe 315, the thermal storage tank 330, the freezing prevention heater 335, the heat wire 335′, the controller 340 and the sensors S and S′ are the same as in the fifth embodiment of the present invention, and an explanation on them will be avoided for the brevity of the description. Therefore, other features of the sixth embodiment of the present invention will be focused herein.

According to the sixth embodiment of the present invention, the hot water intake pipe 323 is connected to the water supply system, and thus, residential water is introduced through the hot water intake pipe 323. A given portion (for example, a portion exposed to external air) of the hot water intake pipe 323 is contacted physically with the hot water discharge pipe 325, and the contacted portion may be surrounded with a heat insulation material.

During the time (for example, night) when the residential water is not used, if the temperature sensed through the sensor S provided on the hot water discharge pipe 325 is below the opening temperature (for example, 4° C.), a freezing prevention valve 328 is open by means of the controller 340, so that the hot water in the thermal storage tank 330 is discharged to the hot water discharge pipe 325 and an outflow pipe 326 communicating with the hot water discharge pipe 325. As a result, the temperatures of the hot water discharge pipe 325 and the given portion (for example, the portion exposed to the external air) of the hot water intake pipe 323 contacted with the hot water discharge pipe 325 are raised to prevent the freezing of the solar water heating system 300.

After that, if the temperature sensed through the sensor S provided on the hot water discharge pipe 325 is above the closing temperature (for example, 10° C.), the freezing prevention valve 328 is closed by means of the controller 340, so that the discharging of the hot water in the thermal storage tank 330 to the hot water discharge pipe 325 and the outflow pipe 326 is prevented. The sensor S is disposed on a given portion exposed to the external air of the hot water discharge pipe 325.

At this time, the lower the temperature of the given portion exposed to the external air of the hot water discharge pipe 325 is below the opening temperature, the larger the degree of opening of the freezing prevention valve 328 is. If necessary, the freezing prevention heater 335 in the thermal storage tank 330 is operated to increase the temperature of the hot water existing in the thermal storage tank 330. In this case, the freezing prevention heater 335 in the thermal storage tank 330 is operated at a temperature higher by 2° C. than the closing temperature and stops at a temperature higher by 4° C. than the closing temperature.

Unlike the fifth embodiment of the present invention, the sensor S is disposed on the hot water discharge pipe 325 having a relatively higher temperature than the hot water intake pipe 323, the opening temperature may be set higher than that in the fifth embodiment of the present invention.

FIG. 16 shows the configuration of a solar water heating system according to a seventh embodiment of the present invention.

According to the seventh embodiment of the present invention, the solar collector 310, the solar collector circulation pipe 315, the thermal storage tank 330, and so on are the same as in the fifth embodiment of the present invention, and an explanation on them will be avoided for the brevity of the description. Therefore, other features of the seventh embodiment of the present invention will be focused herein.

According to the seventh embodiment of the present invention, the hot water intake pipe 323 is connected to the water supply system, and thus, residential water is introduced through the hot water intake pipe 323. A given portion (for example, a portion exposed to external air) of the hot water intake pipe 323 is contacted physically with the hot water discharge pipe 325, and the contacted portion may be surrounded with a heat insulation material. According to the seventh embodiment of the present invention, a freezing prevention valve 329 with a temperature measurement sensor mounted thereon is disposed on an outflow pipe 326, and if the temperature of a portion where the freezing prevention valve 329 is disposed is below the opening temperature (for example, 4° C.), the freezing prevention valve 329 is open by means of the controller 340. On the other hand, if the temperature of the portion where the freezing prevention valve 329 is disposed is above the closing temperature (for example, 10° C.), the freezing prevention valve 329 is closed by means of the controller 340. In more detail, if the temperature sensed by the sensor mounted on the freezing prevention valve 329 is below the opening temperature, the freezing prevention valve 329 is open by means of the controller 340, so that the hot water in the thermal storage tank 330 is discharged to the hot water discharge pipe 325 and the outflow pipe 326, thereby preventing the given portion (for example, the portion exposed to the external air) of the hot water intake pipe 323 from being frozen and destructed. After that, if the temperature sensed by the sensor mounted on the freezing prevention valve 329 is above a given temperature, the freezing prevention valve 329 is closed by means of the controller 340, so that the discharging of the hot water in the thermal storage tank 330 to the hot water discharge pipe 325 and the outflow pipe 326 is prevented.

FIG. 17 shows the configuration of a solar water heating system according to an eighth embodiment of the present invention, FIG. 18 shows the flows of hot water when the solar water heating system of FIG. 17 is operated, FIG. 19 shows the flows of hot water when the solar water heating system of FIG. 17 is operated at night during winter season, and FIG. 20 shows the flows of hot water when the solar water heating system of FIG. 17 is operated during summer season.

Referring to FIG. 18, a solar water heating system 400 according to the eighth embodiment of the present invention includes a thermal storage tank 410, a circulation pump 310, a solar collector 430, a solar collector circulation pipe 440, a thermal storage tank circulation pipe 450, first and second temperature sensors 460 and 470, and a controller 480. In this case, the thermal storage tank 410 and the thermal storage tank circulation pipe 450 are located indoors, and the circulation pump 420, the solar collector 430 and the first temperature sensor 460 are located outdoors.

The thermal storage tank 410 is disposed indoors in such a manner as to be coated with a heat insulation material to prevent heat from being emitted to the outside, while being connected to the thermal storage tank circulation pipe 450 and the solar collector circulation pipe 440. The thermal storage tank circulation pipe 450 is composed of a thermal storage tank intake pipe 451 and a thermal storage tank discharge pipe 452, and the solar collector circulation pipe 440 is composed of a solar collector intake pipe 441 and a solar collector discharge pipe 442. They will be in detail explained below. The thermal storage tank 410 stores the water introduced into the lower portion thereof through the thermal storage tank intake pipe 451, that is, the water used for living (that is, residential water and tap water), and the stored residential water is discharged through the solar collector intake pipe 441. The discharged residential water is heated by the solar collector 430, and the heated residential water is introduced into the upper portion of the thermal storage tank 410 through the solar collector discharge pipe 442. In the preferred embodiment of the present invention, the heated state of the residential water is called hot water. The hot water introduced into the thermal storage tank 410 is discharged through the thermal storage tank discharge pipe 452 and used for living.

The circulation pump 420 is operated by means of the control of the controller 480 and circulates the residential water existing in the lower portion of the thermal storage tank 410 having a relatively lower temperature by 10° C. to 15° C. than the residential water existing in the upper portion thereof.

The solar collector 430 is disposed at the outdoor places such as a top floor or roof of a building, on which a quantity of heat collected is large. The solar collector 430 is connected at one side thereof to the solar collector intake pipe 441 and connected at the other side thereof to the solar collector discharge pipe 442. The solar collector 430 serves to collect solar heat and to heat the residential water supplied through the circulation pump 420, and in this case, various types of solar collectors such as vacuum tube solar collectors, flat plate solar collectors and the like can be used as the solar collector 430.

The solar collector circulation pipe 440 is a closed pipe not connected to the outside, while being located partially inside the solar collector 430. The solar collector circulation pipe 440 connects the solar collector 430 and the thermal storage tank 410 to each other to provide a passage through which the residential water heated by the solar collector 430 is discharged to the thermal storage tank 410. With respect to the solar collector 430, further, the solar collector circulation pipe 440 is composed of the solar collector intake pipe 441 into which the residential water is introduced and the solar collector discharge pipe 442 from which the hot water is discharged. That is, the solar collector intake pipe 441 is adapted to introduce the residential water stored in the thermal storage tank 410 into the solar collector 430, and the solar collector discharge pipe 442 is adapted to introduce the residential water heated by the solar collector 430 into the thermal storage tank 410. Referring to such configuration, the solar collector discharge pipe 442 is disposed at a relatively higher position than the solar collector intake pipe 441, so that the residential water flows along the solar collector intake pipe 441 and the hot water flows along the solar collector discharge pipe 442. This enhances the stratification effect (that is, the water having a relatively high temperature is collected to the upper portion, and the water having a relatively low temperature is collected to the lower portion, thereby supplying good quality of hot water) of the hot water stored in the thermal storage tank 410, so that the residential water introduced into the thermal storage tank 410 is located at the lower portion thereof through the stratification effect, and since the temperature of the hot water located at a relatively high position in the thermal storage tank 410 is higher than that located at a relatively low position, the hot water having the relatively high temperature is used. Even though not shown, also, the portion of the solar collector circulation pipe 440 located in the solar collector 430 should be occupied to a large degree in the interior of the solar collector 430 so as to allow the solar heat collected to the solar collector 430 to be sent completely to water.

The thermal storage tank circulation pipe 450 is connected to the thermal storage tank 410 and serves to provide passages through which the residential water is introduced into the lower portion of the thermal storage tank 410 and the residential water existing in the upper portion of the thermal storage tank 410 is discharged therethrough. The thermal storage tank circulation pipe 450 is composed of the thermal storage tank intake pipe 451 and the thermal storage tank discharge pipe 452. The thermal storage tank intake pipe 451 is connected to the lower portion of the thermal storage tank 410 to perform the stratification of the hot water stored in the thermal storage tank 410, and the thermal storage tank discharge pipe 452 is connected to the upper portion of the thermal storage tank 410.

At this time, as mentioned above, a flow rate of the circulation pump 420 is desirably in a range between 6 l/hr and 9 l/hr per area (1 m²) of the solar collector 430 so as to allow a temperature difference between the upper portion residential water and the lower portion residential water of the thermal storage tank 410 to be in a range between 10° C. and 15° C. The values are obtained by experiments of the present invention, and they are lowered by ⅛ to 1/12 than a generally recommended value of the flow rate of the circulation pump, 72 l/hr per area (1 m²) of a solar collector. Like this, the flow rate becomes lower than the conventional practice, so that the hot water existing a relatively high position in the thermal storage tank 410 and the hot water existing a relatively low position therein are not mixed to each other to allow the temperature difference between the upper portion residential water and the lower portion residential water of the thermal storage tank 410 to be in a range between 10° C. and 15° C., thereby optimizing the stratification effect of the hot water. That is, as the stratification effect of the hot water becomes high, the temperature of the hot water is raised and the temperature of the water introduced into the solar collector 430 is lowered, thereby improving the performance of the solar water heating system 400.

So as to reduce the flow rate of the circulation pump 420, the RPM of the circulation pump 420 may be adjusted or a circulation pump having a small capacity may be installed. For example, if the RPM of the circulation pump 420 becomes reduced by approximately 1/10 than normal RPM, the water flows along the solar collector circulation pipe 440 in the state where the flow rate becomes reduced by 1/10 than normal flow rate.

Referring to FIG. 18, hereinafter, the flow of water when the solar water heating system 400 according to the eighth embodiment of the present invention is operated will be explained. In the drawings, the arrows on the solid line indicate the flow of water.

First, the residential water introduced through the thermal storage tank intake pipe 451 is stored in the thermal storage tank 410, and the solar heat is collected to the solar collector 430, so that the temperature of the solar collector 430 is raised. At this time, the residential water stored in the thermal storage tank 410 is passed through the solar collector intake pipe 441 and is supplied to the solar collector 430 by means of the circulation pump 420. Next, the solar heat collected to the solar collector 430 is sent to the residential water, and the residential water heated through the solar collector 430, that is, the hot water is introduced into the thermal storage tank 410 through the solar collector discharge pipe 442. After that, the hot water introduced into the thermal storage tank 410 is discharged through the thermal storage tank discharge pipe 452 and used in households. In more detail, the residential water before heated flows along the thermal storage tank intake pipe 451 and the solar collector intake pipe 441, and the heated residential water flows along the solar collector discharge pipe 442 and the thermal storage tank discharge pipe 452. In this case, it is appreciated that the flow rate of the circulation pump 420 is limited to a range between 6 l/hr and 9 l/hr per area (1 m²) of the solar collector 430 and reduced by ⅛ to 1/12 than the conventional flow rate. Through the repetition of the above circulation processes, the hot water having a relatively high temperature exists in the upper portion of the thermal storage tank 410, and the hot water having a relatively low temperature exists in the lower portion thereof, so that the temperature difference between the upper portion hot water and the lower portion hot water of the thermal storage tank 410 is in a range between 10° C. and 15° C. Accordingly, the hot water existing a relatively high position in the thermal storage tank 410 and the hot water existing a relatively low position therein are not mixed to each other to optimize the stratification effect of the hot water, so that the hot water having a relatively high temperature can be supplied to the households.

On the other hand, the first temperature sensor 460 is mounted on a given portion of the solar collector circulation pipe 440 located between the circulation pump 420 and the solar collector 430 and serves to detect the temperature of the given portion of the solar collector circulation pipe 440. In this case, the given portion becomes the solar collector intake pipe 441. Mounting the first temperature sensor 460 prevents the solar collector circulation pipe 440 from being frozen and destructed in winter season, and since the residential water having a relatively low temperature is introduced into the solar collector intake pipe 441 and the hot water having a relatively high temperature is discharged to the solar collector discharge pipe 442, the temperature of the solar collector intake pipe 441 is lower than that of the solar collector discharge pipe 442. Further, since a portion exposed to the external air of the solar collector intake pipe 441 has a relatively low temperature, the first temperature sensor 460 desirably measures the temperature on the portion exposed to the external air of the solar collector intake pipe 441.

The second temperature sensor 470 is mounted on the solar collector discharge pipe 442 to detect the temperature thereon. Mounting the second temperature sensor 470 prevents the solar collector 430 or the solar collector discharge pipe 442 from being broken due to overheat in summer season. Since the residential water having a relatively low temperature is introduced into the solar collector intake pipe 441 and the hot water having a relatively high temperature is discharged to the solar collector discharge pipe 442, the temperature of the solar collector discharge pipe 442 is higher than that of the solar collector intake pipe 441. Especially, since a portion exposed to the external air of the solar collector discharge pipe 442 has a relatively high temperature, the second temperature sensor 470 desirably measures the temperature on the portion exposed to the external air of the solar collector discharge pipe 442.

The controller 480 receives the signals produced from the first and second temperature sensors 460 and 470 and controls the activation of the circulation pump 420 in accordance with the received signals.

If the temperature sensed by the first temperature sensor 460 for a given set period of time is below a first reference temperature, first, the circulation pump 420 is activated by means of the controller 480. Contrarily, if the temperature sensed by the first temperature sensor 460 for a given set period of time is above the first reference temperature, the activation of the circulation pump 420 stops by means of the controller 480. In this case, the given set period of time becomes the night time in winter season where temperature drops below zero. Water is always charged in the solar collector circulation pipe 440, and during the time (night) when water is not used, water does not flow along the solar collector circulation pipe 440 and stays therein. According to the properties of water, the volume of water in a solid state (ice) is larger than that in a liquid state, and thus, if the residential water is frozen due to a drop of temperature, it is expanded in volume to cause the solar collector circulation pipe 440 to be frozen and destructed. Since the thermal storage tank 410 is located indoors, however, the temperature of the residential water stored in the thermal storage tank 410 is kept above zero even during the night time in winter season.

Accordingly, if the temperature of the solar collector circulation pipe 440, especially, the solar collector intake pipe 441 is below the first reference temperature, the circulation pump 420 is operated by means of the controller 480, and the residential water having a relatively high temperature stored in the thermal storage tank 410 is circulated along the solar collector circulation pipe 440 to heat the solar collector circulation pipe 440. Through the above process, if the temperature of the solar collector circulation pipe 440 reaches a first set temperature, the activation of the circulation pump 420 stops by means of the controller 480. In the preferred embodiment of the present invention, the first reference temperature for freezing prevention is desirably set to 2° C. The residential water staying in the solar collector circulation pipe 440 in winter season has a temperature higher than the solar collector circulation pipe 440, and since the first temperature sensor 460 is located on the solar collector circulation pipe 440, the detected temperature is lower than that of the residential water existing in the solar collector circulation pipe 440. Therefore, if the circulation pump 420 is operated at the time when the temperature of the solar collector intake pipe 441 is below 2° C., the freezing of the solar collector circulation pipe 440 can be stably prevented.

Based upon the experiments according to the eighth embodiment of the present invention, it is found that if the temperature of the solar collector intake pipe 441 is above 10° C., the freezing of the solar collector circulation pipe 440 is prevented, and accordingly, the first set temperature is desirably set to 10° C. That is, the activation of the circulation pump 420 stops at the time when the temperature of the solar collector intake pipe 441 is above 10° C., which means that since the temperature of the residential water in the solar collector circulation pipe 440 has been already raised, there is no need for further circulation of the residential water.

On the other hand, if the temperature sensed by the second temperature sensor 470 is above a second reference temperature, the circulation pump 420 is activated by means of the controller 480. Contrarily, if the temperature sensed by the second temperature sensor 470 is below a second set temperature, the activation of the circulation pump 420 stops by means of the controller 480. Since the residential water stays in the solar collector 430 or the solar collector circulation pipe 440, generally, the temperature of the solar collector 430 or the solar collector circulation pipe 440 is raised to approximately 100° C. in summer season, especially, at shiny noon, and if there are no overheat radiator and radiator circulation pump, the solar water heating system may be broken due to the excessive temperature rising. In this case, since the temperature of the solar collector discharge pipe 442 is higher than that of the residential water staying therein, desirably, the second reference temperature is set to a range between 93° C. and 98° C. and the second set temperature is set to 80° C. to enhance the reliability in the prevention of the breakage due to overheat. For example, if the temperature of the solar collector discharge pipe 442 is raised to 95° C., the circulation pump 420 is activated by means of the controller 480. Accordingly, the residential water having a relatively low temperature staying in the lower end portion of the thermal storage tank 410 flows along the solar collector 430 and the solar collector circulation pipe 440, and through the repetition of the above process, the temperatures of the solar collector 430 and the solar collector circulation pipe 440 are reduced. If the temperature of the solar collector discharge pipe 442 reaches 80° C., the activation of the circulation pump 420 stops by means of the controller 480.

Further, the controller 480 serves to control the activation of the circulation pump 420 in accordance with the temperature difference sensed by the first and second temperature sensors 460 and 470. Under the control of the controller 480, for example, if the temperature difference is below 3° C., the activation of the circulation pump 420 stops, and if the temperature difference is above 10° C., the circulation pump 420 is activated. As a result, the activation of the circulation pump 420 is controlled normally and the consumption of power is reduced.

Referring to FIG. 19, hereinafter, the flow of water at the time when the solar water heating system 400 is operated during night time in winter season will be explained.

The controller 480 is connected to the first temperature sensor 460 and receives the temperature sensed by the first temperature sensor 460 mounted on the solar collector intake pipe 441. If the sensed temperature is the first reference temperature (2° C.), the circulation pump 420 is activated by means of the controller 480 to allow the water stored in the thermal storage tank 410 to be circulated along the solar collector circulation pipe 440. Through the repetition of the above process, the temperature of the solar collector circulation pipe 440 is raised, and if the temperature of the solar collector intake pipe 441 reaches the first set temperature (40° C.), the activation of the circulation pump 420 stops by means of the controller 480. In winter season, especially, during night time when residential water is not used, the circulation pump 420 is automatically activated to prevent the solar collector circulation pipe 440 from being frozen and destructed.

To do this, just the first temperature sensor 460 is additionally provided to the existing closed type water heating system, thereby enhancing the heat efficiency, simplifying the configuration and installation process, and reducing the possibility of the occurrence of troubles and the maintenance cost thereof. Further, the circulation pump 420 should be activated during night time to prevent the pipe from being frozen in the conventional practice, but in the preferred embodiment of the present invention, the activation and stop of the circulation pump 420 are determined upon the temperature of the solar collector intake pipe 441, thereby substantially reducing a quantity of power consumed. In the preferred embodiment of the present invention, further, since the flow rate of the circulation pump 420 is in a range between 6 l/hr and 9 l/hr per area (1 m²) of the solar collector 430, the staying time of the hot water introduced into the thermal storage tank 410 is extended to allow the heat from the indoor to be sent completely to the hot water and to prevent the temperature of the hot water stored in the thermal storage tank 410 from dropping drastically during the introduction process.

Referring to FIG. 20, next, the flow of water at the time when the solar water heating system 400 is operated in summer season will be explained.

The controller 480 is connected to the second temperature sensor 470 and receives the temperature sensed by the first temperature sensor 470 mounted on the solar collector discharge pipe 442. If the sensed temperature is the second reference temperature (for example, 95° C.), the circulation pump 420 is activated by means of the controller 480 to allow the water stored in the thermal storage tank 410 to be circulated along the solar collector circulation pipe 440. As a result, the hot water having a relatively high temperature staying in the solar collector circulation pipe 440 is introduced into the thermal storage tank 410, and the hot water having a relatively low temperature stored in the thermal storage tank 410 is discharged through the solar collector intake pipe 441. Through the repetition of the above process, the temperature of the solar collector circulation pipe 440 is lowered, and if the temperature of the solar collector discharge pipe 442 reaches the second set temperature (80° C.), the activation of the circulation pump 420 stops by means of the controller 480. Like this, the second temperature sensor 470 is mounted on the solar collector discharge pipe 442 to prevent the solar collector 430 or the solar collector discharge pipe 442 from being broken or degraded due to the rise of temperature in summer season, without having additional overheat radiator and radiator circulation pump, thereby reducing the installation and maintenance costs. As mentioned above, further, since the flow rate of the circulation pump 420 is substantially reduced, the hot water existing a relatively high position in the thermal storage tank 410 and the hot water existing a relatively low position therein are not mixed to each other to enhance the stratification effect of the hot water, so that the hot water having a relatively low temperature flows along the solar collector 430 and the solar collector circulation pipe 440 to allow the temperatures of the solar collector 430 and the solar collector circulation pipe 440 to be lowered efficiently.

As shown in FIGS. 19 and 20, even though conventional complicated configuration and the anti-freezing liquid are not provided, the breakage of the solar water heating system 400, which may be caused by the drop of temperature in winter season and by the rise of temperature in summer season or by the short-term or long-term stop of the operation of the system in summer season, can be prevented, and water is usable as the operating medium, which makes the system very simplified. Moreover, the system can be applied to a heating system having anti-freezing liquid or water as the operating medium, and just one circulation pump 420 is activated without having any overheat radiator and radiator circulation pump to allow the heat to be absorbed to the thermal storage tank 410, thereby easily preventing overheating. Instead of anti-freezing liquid, water is charged in the solar collector 430 and the solar collector circulation pipe 440, thereby reducing the maintenance cost and easily performing the maintenance thereof.

As described above, according to the present invention, the freezing prevention valves (or the circulation pump) and the freezing prevention heater are operated by means of the controller in accordance with the variation of only the temperature T1 of the hot water discharge pipe or the variation of at least one or more of the temperature T1 of the hot water discharge pipe and the temperature T2 of the water in the thermal storage tank, so that the water having a relatively high temperature stored in the thermal storage tank is moved along the hot water circulation pipe, thereby increasing the temperature of the water thereinto.

With the simple configuration of the solar water heating system according to the present invention, accordingly, the freezing of the hot water circulation pipe in winter season can be prevented, thereby enhancing the heat efficiency of the system, and no additional heat wire is needed to adjust the temperature of the hot water circulation pipe, thereby more simplifying the configuration of the system.

Further, the temperature of the hot water circulation pipe is adjusted by using the hot water in the thermal storage tank, thereby reducing the maintenance cost of the solar water heating system.

Furthermore, the freezing prevention heater is operated in accordance with the variations of the temperature T1 of the hot water discharge pipe and the temperature T2 of the water stored in the thermal storage tank, thereby remarkably reducing the quantity of electricity consumed and decreasing the maintenance cost of the solar water heating system.

Additionally, when the temperature of the hot water intake pipe of the hot water circulation pipe drops below the opening temperature during the time when hot water is not used and the flow of water stops in the system, the first and second freezing prevention valves are open, and the third freezing prevention valve is closed, so that a given quantity of hot water in the inside tank is discharged through the hot water circulation pipe, that is, the hot water intake pipe and the hot water discharge pipe. The hot water in the inside tank is a relatively hot water heat-exchanged with the operating medium, which flows along the hot water circulation pipe and is discharged to the outside, thereby raising the temperature of the hot water circulation pipe and preventing the hot water circulation pipe from being frozen and destructed.

Moreover, if the temperature of the inside tank in the thermal storage tank drops below the opening temperature, the freezing prevention heater is operated to raise the temperature above the closing temperature, thereby preventing the inside tank from being frozen and destructed. At this time, the hot water in the inside tank is discharged to the outside, thereby being decreased in quantity and preventing the inside tank from being frozen and destructed due to the rapid drop of the temperature of the inside tank.

In addition, in winter season, especially, during night time when residential water is not used, the circulation pump is automatically activated to prevent the solar collector circulation pipe from being frozen and destructed. To do this, just the first temperature sensor is additionally provided to the existing closed type water heating system, thereby enhancing the heat efficiency, simplifying the configuration and installation process, and reducing the possibility of the occurrence of troubles and the maintenance cost thereof.

Further, the second temperature sensor is mounted on the solar collector discharge pipe to prevent the solar collector or the solar collector discharge pipe from being broken or degraded due to the rise of temperature in summer season, without having any overheat radiator and radiator circulation pump, thereby reducing the installation and maintenance costs thereof.

Also, the flow rate of the circulation pump is desirably in a range between 6 l/hr and 9 l/hr per area (1 m²) of the solar collector 430 so as to allow a temperature difference between the upper portion residential water and the lower portion residential water of the thermal storage tank to be in a range between 10° C. and 15° C., thereby optimizing the stratification effect of the hot water and improving the performance of the solar water heating system.

Instead of anti-freezing liquid, further, water is charged in the solar collector and the solar collector circulation pipe, thereby reducing the maintenance cost and easily performing the maintenance thereof.

While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention. 

1. A solar water heating system comprising: a solar collector to which solar heat is collected; a solar collector circulation pipe connected to the solar collector and adapted to circulate an operating medium on which the solar heat collected by the solar collector is accumulated therealong; a thermal storage tank in which the operating medium and the water used for living are heat-exchanged; a hot water circulation pipe communicating with the thermal storage tank, to which the water is supplied; a freezing prevention valve located on one side of the hot water circulation pipe and adapted to be selectively open and closed to allow the water in the thermal storage tank to selectively flow along the hot water circulation pipe; and a controller adapted to control the operation of the freezing prevention valve in accordance with the variation of at least one or more of a temperature T1 of a given portion of the hot water circulation pipe and a temperature T2 of the water in the thermal storage tank, thereby preventing the hot water circulation pipe from being frozen and destructed.
 2. The solar water heating system according to claim 1, wherein if the temperature T1 of a given portion of the hot water circulation pipe is below Ta (wherein 1° C≦Ta≦6° C.), the freezing prevention valve is open by means of the controller, and if the temperature T1 of the given portion of the hot water circulation pipe is above Tc (wherein 9° C≦Tc≦11° C.), the freezing prevention valve is closed by means of the controller.
 3. The solar water heating system according to claim 1, wherein if the temperature T1 of a given portion of the hot water circulation pipe is below Ta (wherein 3° C≦Ta≦6° C.), the freezing prevention valve is open by means of the controller, and if the temperature T1 of the given portion of the hot water circulation pipe and the temperature T2 of the water of the thermal storage tank satisfy the condition (1), T2>Tb, T1>Tc and the condition (2), T2≦Tb, T1>T2−dT (wherein 11° C<Tb≦14° C., 9° C≦Tc≦11° C., 1° C≦dT≦3° C.), the freezing prevention valve is closed by means of the controller.
 4. The solar water heating system according to claim 2 or 3, wherein the Ta is 4° C., the Tb is 12° C., the Tc is 10° C., and the dT is 2° C.
 5. A solar water heating system comprising: a solar collector to which solar heat is collected; a solar collector circulation pipe connected to the solar collector and adapted to circulate an operating medium on which the solar heat collected by the solar collector is accumulated therealong; a thermal storage tank in which the operating medium and the water used for living are heat-exchanged; a hot water circulation pipe communicating with the thermal storage tank and having a hot water intake pipe through which the water is supplied to the thermal storage tank and a hot water discharge pipe through which the water is discharged from the thermal storage tank; a connection pipe adapted to allow the hot water intake pipe and the hot water discharge pipe to communicate with each other; a check valve mounted on the connection pipe and adapted to selectively open and close the connection pipe; a circulation pump mounted on the connection pipe and adapted to allow the water in the thermal storage tank to be circulated along the hot water intake pipe and the hot water discharge pipe through the connection pipe; and a controller adapted to control the operation of the circulation pump in accordance with the variation of at least one or more of a temperature T1 of a given portion of the hot water circulation pipe and a temperature T2 of the water in the thermal storage tank, thereby preventing the hot water circulation pipe from being frozen and destructed.
 6. The solar water heating system according to claim 5, wherein if the temperature T1 of a given portion of the hot water circulation pipe is below Ta (wherein 1° C≦Ta≦6° C.), the circulation pump is operated by means of the controller, and if the temperature T1 of the given portion of the hot water circulation pipe and the temperature T2 of the water of the thermal storage tank satisfy the condition (1), T2>Tb, T1>Tc and the condition (2), T2≦Tb, T1>T2−dT (wherein 11° C<Tb≦14° C., 9° C≦Tc≦11° C., 1° C≦dT≦3° C.), the operation of the circulation pump stops by means of the controller.
 7. The solar water heating system according to claim 6, wherein the Ta is 2° C., the Tb is 12° C., the Tc is 10° C., and the dT is 2° C.
 8. The solar water heating system according to claim 6, further comprising a freezing prevention heater adapted to adjust the temperature of the water in the thermal storage tank under the control of the controller, wherein if the temperature T2 of the water of the thermal storage tank is below 12° C., the freezing prevention heater is operated by means of the controller, and if the temperature T2 of the water of the thermal storage tank is above 14° C., the operation of the freezing prevention heater stops by means of the controller.
 9. The solar water heating system according to claim 5 or 6, further comprising a freezing prevention heater adapted to adjust the temperature of the water in the thermal storage tank under the control of the controller, wherein if the temperature T2 of the water of the thermal storage tank is below 6° C., the freezing prevention heater is operated by means of the controller, and if the temperature T2 of the water of the thermal storage tank is above 8° C., the operation of the freezing prevention heater stops by means of the controller.
 10. A solar water heating system comprising: a solar collector to which solar heat is collected; a solar collector circulation pipe connected to the solar collector and adapted to circulate an operating medium on which the solar heat collected by the solar collector is accumulated therealong; a thermal storage tank having an outside tank communicating with the solar collector circulation pipe and an inside tank located inside the outside tank in such a manner as to be isolated from the outside tank; a hot water circulation pipe communicating with the inside tank, to which the water is supplied; one or more freezing prevention valves adapted to be open and closed if a given portion of the hot water circulation pipe reaches an opening temperature, to allow the water in the inside tank to be discharged to the outside from the hot water circulation pipe and adapted to be open and closed if the given portion of the hot water circulation pipe reaches a closing temperature, to prevent the water in the inside tank from being discharged to the outside from the hot water circulation pipe; and a controller adapted to control the opening/closing of the one or more freezing prevention valves in accordance with the variation of the temperature of the given portion of the hot water circulation pipe, thereby preventing the hot water circulation pipe from being frozen and destructed.
 11. The solar water heating system according to claim 10, wherein the hot water is residential water, the hot water circulation pipe has a hot water intake pipe through which the residential water is introduced into the inside tank and a hot water discharge pipe through which the residential water heated in the inside tank is discharged, the hot water discharge pipe being partially contacted with the hot water intake pipe, the given portion of the hot water circulation pipe is a portion of the hot water discharge pipe, on which a sensor measuring the temperature of the given portion is mounted, the hot water discharge pipe having an outflow pipe mounted on one side thereof to discharge the hot water to the outside of the hot water circulation pipe, and the freezing prevention valve is mounted on the outflow pipe to open and close the outflow pipe.
 12. The solar water heating system according to claim 11, further comprising a heat insulation material adapted to be surrounded along the contacted portion between the hot water intake pipe and the hot water discharge pipe.
 13. The solar water heating system according to claim 10, wherein the hot water is residential water, the hot water circulation pipe has a hot water intake pipe through which the residential water is introduced into the inside tank and a hot water discharge pipe through which the residential water heated in the inside tank is discharged, the hot water intake pipe and the hot water discharge pipe having first and second outflow pipes mounted on one sides thereof to discharge the hot water to the outside of the hot water circulation pipe, and the freezing prevention valves are composed of a first freezing prevention valve mounted on the first outflow pipe to open and close the first outflow pipe, a second freezing prevention valve mounted on the second outflow pipe to open and close the second outflow pip, and a third freezing prevention valve mounted on the hot water intake pipe in such a manner as to be closed if the first freezing prevention valve is open and to be open if the first freezing prevention valve is closed.
 14. The solar water heating system according to claim 11 or 13, further comprising a freezing prevention heater disposed at the inside tank to raise the temperature of the hot water in the inside tank, the freezing prevention heater being operated by means of the controller if the given portion of the hot water circulation pipe reaches the opening temperature and the operation of the freezing prevention heater being stopped by means of the controller if the given portion of the hot water circulation pipe reaches the closing temperature.
 15. A solar water heating system comprising: a solar collector to which solar heat is collected; a solar collector circulation pipe connected to the solar collector and adapted to circulate an operating medium on which the solar heat collected by the solar collector is accumulated therealong; a thermal storage tank having an outside tank communicating with the solar collector circulation pipe and an inside tank located inside the outside tank in such a manner as to be isolated from the outside tank; a hot water circulation pipe communicating with the inside tank and having a hot water intake pipe through which residential water is introduced into the inside tank and a hot water discharge pipe through which the residential water heated in the inside tank is discharged, the hot water discharge pipe being partially contacted with the hot water intake pipe; an outflow pipe mounted on one side of the hot water discharge pipe to discharge the hot water to the outside of the hot water circulation pipe; and a freezing prevention valve having a sensor mounted thereon to measure a temperature in such a manner as to open and close the outflow pipe in accordance with the temperature sensed by the sensor.
 16. A solar water heating system comprising: a thermal storage tank in which residential water introduced thereinto is stored; a circulation pump adapted to circulate the residential water existing in the lower portion of the thermal storage tank having a lower temperature by 10° C. to 15° C. than the residential water existing in the upper portion of the thermal storage tank therethrough; a solar collector to which solar heat is collected to heat the residential water supplied by the circulation pump; a solar collector circulation pipe adapted to connect the solar collector and the thermal storage tank with each other and adapted to provide a passage through which the residential water heated by the solar collector is discharged to the thermal storage tank; a thermal storage tank circulation pipe connected to the thermal storage tank and adapted to provide passages through which the residential water is introduced into the lower portion of the thermal storage tank and the residential water existing in the upper portion of the thermal storage tank is discharged; a first temperature sensor mounted on the thermal storage tank circulation pipe to detect the temperature thereon; and a controller adapted to operate the circulation pump if the temperature detected by the first temperature sensor is below a first reference temperature, wherein the thermal storage tank and the thermal storage tank circulation pipe are located indoors, and the circulation pump, the solar collector and the first temperature sensor are located outdoors.
 17. The solar water heating system according to claim 16, wherein the solar collector circulation pipe comprises a solar collector intake pipe adapted to provide a passage through which the residential water stored in the thermal storage tank is introduced into the solar collector and a solar collector discharge pipe adapted to provide the passage through which the residential water heated by the solar collector is discharged to the thermal storage tank, and the first temperature sensor is mounted on the solar collector intake pipe in vicinity of the solar collector.
 18. The solar water heating system according to claim 17, further comprising a second temperature sensor mounted on the solar collector discharge pipe in vicinity of the solar collector, and the circulation pump is operated by means of the controller if the temperature detected by the second temperature sensor is above a second reference temperature.
 19. The solar water heating system according to claim 18, wherein the operation of the circulation pump stops by means of the controller if the temperature detected by the first temperature sensor or the second temperature sensor is above a first set temperature or below a second set temperature.
 20. The solar water heating system according to claim 16, wherein a flow rate of the circulation pump is in a range between 6 l/hr and 9 l/hr per area (1 m²) of the solar collector.
 21. The solar water heating system according to claim 18, wherein the circulation pump is operated by means of the controller in accordance with the difference between the temperatures detected by the first temperature sensor and the second temperature sensor. 